DESCRIPTION (Adapted from the application): The calcium hypothesis of AD, advanced over 12 years ago postulates that sustained disturbances in intracellular calcium regulation are a primary cause of AD neurodegeneration. Consistent with this hypothesis, changes in intracellular calcium not only mediate neuronal cell death, but also increase production of beta amyloid, which accumulates in diffuse and neuritic plaques, a hallmark feature of AD. Although these and other findings suggest that perturbed calcium homeostasis lies upstream of the amyloid cascade, this issue is still widely debated. With the identification of genes causally linked to AD, namely, presenilin-l and -2 (PSI and PS2), it is now possible to dissect the molecular and cellular events responsible for these changes in cultured cells and transgenic animals. The preliminary data show that several different AD-linked mutations in both PS 1 and PS2 all potentiate the phosphoinositide intracellular calcium signaling pathway at the level of calcium release from the endoplasmic reticulum. The first aim will establish whether multiple presenilin mutations share the common feature of altering intracellular calcium signaling. The second aim will test several specific hypotheses about the mechanisms underlying presenilins effects on this pathway. The investigators also have preliminary data suggesting that the presenilins may affect other intracellular calcium signaling pathways, including capacitative calcium entry, disturbances which may be an early and reliable diagnostic marker of familial AD. The third aim of this study examines the potential involvement of the presenilins in this and other intracellular calcium signaling pathways. The proposed experiments will use advanced molecular and pharmacological methods in combination with high-resolution microscopy. Experiments will be conducted in a range of cell types, including Xenopus oocytes, cultured cell lines, and will also feature the use of primary neurons isolated from mutant PSI knock-in animals, which represent the most advanced reagent available for the study of presenilin mutations. Data generated from these experiments are expected to significantly increase the understanding of presenilin function and could uncover novel targets for the early diagnosis and/or therapeutic intervention of AD.